Living rhodolith beds in the Gulf of California and their implications for paleoenvironmental interpretation,

Description

Subtidal surveys in the southwestern Gulf of California indicate that rhodolith beds are widely distributed, major sources of carbonate sediments, and habitats of high biodiversity. Beds with abundant branched rhodoliths ranging in size from 2 to 10 cm (longest dimension) have been found in two main types of environments: (1) gently sloping, subtidal soft bottoms with moderate wave action (wave beds; 2 to 12 m deep), and (2) relatively level bottoms in channels with tidal currents (current beds; below 12 m). Large individuals (to 11 cm) with up to 1 cm thick, densely packed branches are also found dispersed among sand and cobbles on more wave exposed shores. The relative abundance of fruticose forms and the sphericity and branch density of individual thalli are generally higher in wave beds than in current beds. Morphology within wave beds varies along gradients of water motion, with higher branch densities, more apical branching, and more branch fusions present as water motion increases. The extent to which these morphological differences represent different taxa is being evaluated. The abundance of rhodoliths in Pliocene and Pleistocene carbonate deposits and modern sediments indicates that this community has long been an important feature of nearshore environments in the Gulf. Our results suggest that measurements of a combination of morphological characters in populations of fossil rhodoliths, combined with detailed, small-scale stratigraphic analyses, may provide good estimates of paleoenvironmental conditions., Cited By (since 1996):6, Seaweeds, ,

Variability in per capita oogonia and sporophyte production from giant kelp gametophytes (Macrocystis pyrifera, Phaeophyceae)

Description

Vegetative growth and fertility of kelp gametophytes are thought to be antagonistic, such that most successful kelp recruitment is assumed to result from fertilization of single oogonia released from unicellular female gametophytes. We used laboratory culture experiments to study the effect of temperature and nutrient addition on the per capita production of oogonia and sporophytes from Macrocystis pyrifera female gametophytes. Our results indicate that individual multicellular female gametophytes can give rise to more than one oogonium and that per capita oogonia production significantly increases with the enhancement of culture conditions (i.e., decreased temperature and increased nutrient concentration). Furthermore, the production of multiple oogonia per female often led to the production of multiple sporophytes per female. We discuss the importance of these results relative to variability in M. pyrifera life histories (e.g., annual vs. perennial) and their likely ecological and evolutionary consequences., Cited By (since 1996):11, Seaweeds

The kelp highway hypothesis: Marine ecology, the coastal migration theory, and the peopling of the Americas

Description

In this article, a collaborative effort between archaeologists and marine ecologists, we discuss the role kelp forest ecosystems may have played in facilitating the movement of maritime peoples from Asia to the Americas near the end of the Pleistocene. Growing in cool nearshore waters along rocky coastlines, kelp forests offer some of the most productive habitats on earth, with high primary productivity, magnified secondary productivity, and three-dimensional habitat supporting a diverse array of marine organisms. Today, extensive kelp forests are found around the North Pacific from Japan to Baja California. After a break in the tropicswhere nearshore mangrove forests and coral reefs are highly productivekelp forests are also found along the Andean Coast of South America. These Pacific Rim kelp forests support or shelter a wealth of shellfish, fish, marine mammals, seabirds, and seaweeds, resources heavily used historically by coastal peoples. By about 16,000 years ago, the North Pacific Coast offered a linear migration route, essentially unobstructed and entirely at sea level, from northeast Asia into the Americas. Recent reconstructions suggest that rising sea levels early in the postglacial created a highly convoluted and island-rich coast along Beringia's southern shore, conditions highly favorable to maritime hunter-gatherers. Along with the terrestrial resources available in adjacent landscapes, kelp forests and other nearshore habitats sheltered similar suites of food resources that required minimal adaptive adjustments for migrating coastal peoples. With reduced wave energy, holdfasts for boats, and productive fishing, these linear kelp forest ecosystems may have provided a kind of kelp highway for early maritime peoples colonizing the New World., Cited By (since 1996):22, Seaweeds

Cited By (since 1996):19
Seaweeds, CODEN: MESED, In March 1989, the 'Exxon Valdez' spilled over 10 million gallons (ca 38 million I) of crude
oil into Prince William Sound, Alaska , USA. The spill was followed by massive clean-up using hot seawater
at high pressure as well as other mechanical and chemical techniques. We studied initial damage
and subsequent recovery in the upper margin of the Fucus gardneri assemblage on protected shores by
comparing sites that were unoiled, oiled and cleaned with hot water at high pressure, and oiled but less
intensely cleaned. F. gardneri cover averaged 80% on unoiled sites but< 1 % on all oiled and cleaned
sites 18 mo after the spill. The abundances of barnacles, littorine snails and limpets varied among sites
and species, and this variation was associated in part with differences in their life histories. F. gardneri
cover was still extremely low on oiled and cleaned sites 2.5 yr after the spill. Holdfasts that persisted
after cleaning did not resprout. F. gardneri recruitment was lowest at intensely cleaned sites, and most
recruits occurred in cracks near adults. Recruits were less abundant under adult canopies but placing
canopies over recruits did not decrease their survivorship over 5 mo. Natural weathering of tar was
rapid, with most marked patches gone in less than 1 yr. We conclude that intense mechanical cleaning
following this oil spill increased damage and slowed recovery. Such methods should be avoided if
reduction of environmental damage is the primary objective of post-spill management decisions. The
recovery of F. gardneri at its upper margin might be enhanced by devices that retain moisture and
increase substratum rugosity., ,

Evolution of Macrocystis spp. (Phaeophyceae) as determined by ITS1 and ITS2 sequences

Description

Macrocystis (Lessoniaceae) displays an antitropical distribution, occurring in temperate subtidal regions along western North America in the northern hemisphere and throughout the southern hemisphere. We used the noncoding rDNA internal transcribed spacer regions (ITS1 and ITS2) to examine relatedness among (1) Macrocystis and several genera of Laminariales, (2) four species of Macrocystis (M. integrifolia Bory from the northern hemisphere, M. angustifolia Bory and M. laevis Hay from the southern hemisphere, and M. pyrifera [L.] C. Ag. from both hemispheres), and (3) multiple clones of several individuals. Of the taxa included in our phylogenetic analysis, the elk kelp, Pelagophycus porra (Lem.) Setch., was the sister taxon to Macrocystis spp. Macrocystis individuals from the southern hemisphere (representing three species) formed a strongly to moderately supported clade, respectively, when the ITS1 and ITS2 sequences were analyzed separately. No distinction was detected between the two species in the northern hemisphere. Thus, Macrocystis may be a monospecific genus (M. pyrifera). A northern-hemisphere-to-southern-hemisphere pattern of dispersal was inferred, because northern-hemisphere individuals were more diverse and displayed paraphyletic clades, whereas southern-hemisphere individuals were less diverse and formed a monophyletic clade. High intraindividual variation in ITS1 sequences was observed in one individual from Santa Catalina Island (CA), suggesting very recent and rapid mixing of genotypes from areas to the north and Baja California (Mexico) or introgressive hybridization with Pelagophycus., Cited By (since 1996):67, Seaweeds, CODEN: JPYLA

The effects of insolation and grazing on populations of the splash zone alga Prasiola meridionalis (Chlorophyta),

Description

Field experiments at two sites assessed the effects of insolation and gastropod grazing on the distribution and abundance of Prasiola meridionalis Setchell et Gardner, a green alga that occurs in the upper splash zone (supralittoral) on guano-covered rocks. At site 1, a sun-exposed horizontal rock where the alga occurs seasonally and grazers were rare, blades appeared in the early spring and died back in early summer. Lack of gastropod grazers and persistence of blades in experimentally shaded plots showed that increased insolation or some associated factor (or factors) was responsible for temporal variation at this site. At site 2, the alga grew in a distinct, perennial band on a shaded vertical rock face with abundant gastropod grazers. These grazers were excluded from long vertical plots that extended from the lower portion of the P. meridionalis band down to a zone of the red alga Endocladia muricata (Postels et Ruprecht) J. Agardh more than 2 m below. The results showed that grazing set the proximate lower limit of P. meridionalis at site 2, and variation in the abundance of the alga within its zone at this site was associated with seasonal climate changes and feeding by mites. Thus, while insolation and grazing can both affect populations of P. meridionalis, their relative importance varied between sites., Cited By (since 1996):4, Seaweeds, CODEN: PYCOA, ,

Effects of shade from multiple kelp canopies on an understory algal assemblage,

Description

We examined the effects of shade from multiple kelp canopy layers (surface Macrocystis pyrifera canopy, understory Pterygophora californica canopy), both individually and in combination, on an understory algal assemblage in a central Californian kelp forest. The removal of both kelp canopies resulted in a dense recruitment of the understory brown alga Desmarestia ligulata that formed a third canopy layer, which significantly decreased bottom light and the abundance of understory red algae. We subsequently created an additional canopy treatment by removing this third canopy layer. In general, the understory red algae fluctuated seasonally with winter swell intensity, changes in kelp canopy cover, and grazing; and although species richness increased significantly with increased bottom light, red algal bottom cover did not respond significantly to the canopy clearings until 2 yr after the canopies were initially cleared. Red algal cover within the Pterygophora canopy treatment was similar to that in the control treatment. In the absence of Pterygophora, the Macrocystis canopy treatment and 'no canopy' treatment were found to have greater red algal cover and species richness. Individual understory species were rare, which resulted in small effects sizes and thus low statistical power. However, when grouped post hoc, according to how they responded to the canopy clearings (i.e. response groups), we were able to detect canopy treatment effects as much as 1 yr earlier. This method identified that some understory red algae adapted to areas of canopy removal (light-adapted), and others adapted to a variety of light regimes (shade-tolerant). We were able to classify the light-adapted algae into 2 subgroups: the high-light species and the intermediate-light species. Although this method of grouping was done post hoc, our results indicate that it may provide the clearest assessment of how understory algae respond to shading from kelp canopies., Cited By (since 1996):40, Seaweeds, CODEN: MESED, ,

A cDNA-encoding glutamime synthetase (GS) was isolated from the marine diatom Skeletonema costatum (Greville) Cleve by PCR amplification. Nucleic acid and deduced amino acid sequences of the diatom GS were greater than 50% identical to GS from green algae and vascular plants, and phylogenetic analysis established the diatom GS as a member of the GSII gene family. The presence of an N-terminus signal sequence, identified on the basis of sequence similarity with other chloroplast-localized proteins from diatoms, suggests that the encoded GS isoenzyme is localized to the chloroplast. The GS mRNA was present in log-phase cells grown with either nitrate or ammonium as the sole added nitrogen source. Results from Southern blot analysis of genomic DNA suggested that the cDNA isolated in this study was either a member of a small, highly conserved gene family or that there was allelic variation within the region examined. Phylogenetic analyses further indicated that genes encoding GS from the diatom and two species of green algae diverged prior to the gene duplication, to the isoenzymes in vascular plants, supporting the hypothesis that GS isoenzymes in diatoms, green algae, and vascular plants arose through independent evolutionary events., Cited By (since 1996):16,
Seaweeds, CODEN: JPYLA, ,

Recreational SCUBA diving has greatly increased in the past 20 years and has potential to cause significant disturbances to subtidal reefs. While diver disturbance on coral reefs has been assessed in a number of studies, disturbances in temperate kelp forests have not been previously examined. We estimated diver disturbance in southern Monterey Bay giant kelp, Macrocystis pyrifera, forests by following 42 divers in summer 1997 and recording their activity. During a 0.5 hour dive, the average diver contacted the bottom 43 times, touched 4 animals, and detached 2 algal blades. An estimated 65,000 diver-days are spent in these kelp forests every year, resulting in a potential loss of 130,000 algal blades and considerable benthic disturbances. The effects of these impacts and mitigation for them should be considered in proposals to establish and manage marine protected areas., Cited By (since 1996):2, Ecology,
Seaweeds, ,

Experiments in a central California Macrocystis pyrifera (L.) C.A. Agardh forest examined the effects of long-term (six year) kelp canopy exclusion on the abundance of the annual brown alga Desmarestia ligulata (Light F). Exclusion of both surface and subsurface kelp canopies from replicate clearings within stillwater Cove, CA, USA showed that D. ligulata sporophyte recruitment is opportunistic, with more sporophytes occurring in areas where canopies were excluded than under control canopies. Kelp canopy exclusion also increased spring and summer bottom irradiances, and resulted in a steady increase of perennial turf algae over the six-year study. This, in turn, led to a decrease in the availability of nongeniculate coralline algae (the primary substratum on which D. ligulata recruits). Subsequently, the annual maximum abundance of D. ligulata sporophytes decreased in the Canopy clearings, but did not change under control canopies. Removal of turf algae from experimental plots further increased bottom irradiances and significantly enhanced D. ligulata recruitment. When released from apparent competition for light and space, D. ligulata sporophytes exhibited an annual life history, with recruitment occurring during a two-week period (April 4- April 17) in the spring, and maximum bottom cover occurring in the summer (July). The onset of Desmarestia sporophyte recruitment was closely associated with seasonal increases in daylength and rapid decreases in ocean temperature. These results indicate that the Desmarestia sporophyte life history is both annual and opportunistic, with the onset of recruitment stimulated by predictable, seasonal changes in environmental conditions, and the magnitude of recruitment modified by stochastic processes that affect the availability of light and space. Comparison of these results with those from similar studies indicate that they are robust and suggest that they may be generalized over broad temporal and spatial scales., Cited By (since 1996):43, Seaweeds, CODEN: JEMBA, ,

The deep-water macroalgal assemblage was described at 14 sites off the central California coast during 1999 and 2000 from SCUBA and remotely operated vehicle sampling. The stipitate kelp Pleurophycus gardneri Setchell & Gardner, previously thought to be rare in the region, was abundant from 30 to 45 m, forming kelp beds below the well-known giant kelp forests. Macroalgae typically formed three broadly overlapping zones usually characterized by one or a few visually dominant taxa: 1) the upper "Pleurophycus zone" (30-45 m) of stipitate kelps and Desmarestia spp. with a high percent cover of corallines, low cover of uncalcified red algae, and rare green algae; 2) a middle "Maripelta zone" (40-55 m) with other uncalcified red algae and infrequent corallines and green algae; and 3) a zone (55-75 m) of infrequent patches of non-geniculate coralline algae. The green alga Palmophyllum umbracola Nelson & Ryan, not previously reported from the Northeast Pacific, was found over the entire geographical range sampled from 35 to 54 m. Year-round profiles of water column irradiance revealed unexpectedly clear water with an average K0 of 0.106·m-1. The low percent surface irradiance found at the average lower macroalgal depth limits in this study (0.56% for brown algae, 0.12% for uncalcified red algae, and 0.01% for nongenictilate coralline algae) and lack of large grazers suggest that light controls the lower distributional limits. The ubiquitous distribution, perennial nature, and similar lower depth limits of deep-water macroalgal assemblages at all sites suggest that these assemblages are a common persistent part of the benthic biota in this region., Cited By (since 1996):26
Seaweeds, CODEN: JPYLA, ,

Using in situ substratum sterilization and fluorescence microscopy in studies of microscopic stages of marine macroalgae,

Description

The methods currently used for examining the relative contribution of microscopic stages to the persistence of natural populations of marine macroalgae can be inappropriate for use in subtidal habitats. Also, because of their microscopic size, direct examination and obtaining an estimate of recruitment, growth and mortality of these stages in the field is difficult. A method of removing microscopic algal stages from natural rock surfaces using watertight tents and water-soluble chemicals is presented. Also discussed is the use of a previously described method of fluorescent labelling these microscopic stages that, when examined under UV light, allows for their precise identification and growth to be determined. Together, these methods can be effective in examining the ecology of algal microscopic stages in the field., Cited By (since 1996):1, Seaweeds, CODEN: HYDRB, ,

Delayed recruitment of microscopic stages in respouse to cyclical cues is critical to the population dynamics of many annual and seasonally reproducing perennial seaweeds. Microscopic stages may play a similar role in continuously reproducing perennials in which adult sporophytes are subject to episodic mortality, if they can respond directly to the unpredictable onset and relaxation of unfavorable conditions. We experimentally evaluated the potential for temporary reduction in limiting resources (light, nutrients) to directly delay recruitment of giant kelp (Macrocystis pyrifera (L.) C.A. Agardh) gametophytes and embryonic sporophytes. Laboratory cultures were subjected to limiting conditions of light and nutrients for 1 month and then exposed to non-limiting conditions for 10 days. Gametophytes in all treatments failed to recruit to sporophytes after 2 weeks, suggesting they are not a source of delayed recruitment in giant kelp. Sporophytes in light-limited treatments, however, survived and grew significantly slower than non-light-limited controls. When stimulated with light, light-limited sporophytes grew from 2 to >10 times faster than unstimulated controls depending on nutrient availability. These results suggest that limiting resources can delay recruitment of embryonic giant kelp sporophytes for at least 1 month. Flexible timing of recruitment from embryonic sporophytes may enhance persistence of continuously reproducing perennial species when macroscopic adults are subject to episodic large-scale removals., Cited By (since 1996):24,
Seaweeds, CODEN: JPYLA